1. Field of the Invention
The invention relates to a method and apparatus for discharging slag from gasification reactors. The invention is suited for discharging slag from reactors during gasification of ash-containing fuels. The invention can be used with any type of gasifier in which ash or slag is discharged from a pressure system.
2. The Prior Art
During pressure gasification of ash-containing fuels in dust form, in lumps or in liquid form, solid residues are formed from the fuel ash as a function of the gasification temperature, said residues being formed either in the form of slightly molten granulated ash or in the form of fully molten slag and being evacuated from the pressure systems after cooling. Fuel in dust form, in lumps or in liquid form is understood to refer to conventional fuels such as coals of various ranks, cokes of various origin, but also to solids-containing oils and tars as well as slurries that may be utilized as coal-water or coal-oil slurries or slurries obtained in the form of suspensions of pyrolysis coke and pyrolysis liquids from thermal pre-treatment using different pyrolysis methods of biomass.
Generally, the granulated ash or fully molten slag is cooled by injecting water and is collected in bulk form in a water bath, discharged from the pressure system through pressure lock hoppers and disposed of, or processed, into building materials.
Such type methods and apparatus are described in European Patent No. EP 0 545 241 B1 and German Patent No. DE 4 109 231. EP 0 545 241 B1 describes a method for thermal utilization of waste materials, combining actually known process steps such as pyrolysis, comminution, classification, gasification and gas purification in which CO— and H2-containing gas and a slag are formed in a gasification reactor, the slag granulating upon contact with water and being discharged from the gasification reactor.
DE 4 109 231 C2 describes a method of recycling halogen-loaded, carbon-containing waste materials by which waste materials are converted in the entrained flow, according to the principle of partial oxidation, to a carbon monoxide- and hydrogen-containing crude gas. There is a water bath, in which the solidifying slag particles are received and discharged from the pressure reactor through a lock hopper, being disposed in the lower part of the reactor.
This technology has major disadvantages leading to operation failures and limiting the availability of the technology as a whole. Such failures are e.g., due to the solidification of the ashes/slags in the water bath, which is promoted by the solid substances forming in a wide range of grain sizes. The solidification leads to the formation of bridges and blocks the evacuation process.
The ashes/slags are cooled at gasification pressures of up to 80 bar at temperatures of up to between 150 and 250° C., water vapor forming during evacuation as a result of the expansion. Gases such as CO2 and H2S simultaneously escaping from the pressure system during the expansion of the ash/slag/water mixture result in a toxic contamination of this water vapor therewith and secure cooling is complicated.